Reflection probability – Laser light at the beam splitter

A continuous laser beam throws a red point on the wall. In the laser beam, we place a beam splitter. As a result, we obtain a second red point on the wall.

With the helium neon laser used – wavelength equal to 632 nanometres – with the output being one milliwatt, 0.3 x 10^16 individual photons per second hit the beam splitter cube. Of these N photons, 50% are reflected and 50% transmitted. That means that the reflection and transmission intensity are both proportional to N/2. To understand quantum randomness in transmission and reflection, we need to use a specific light source that is able to generate individual photons in a controlled manner.